The proposed research is a study of the response of single neurons in the lateral geniculate nucleus (LGN) and fibers in the optic tract (OT)of the cat to the velocity of stimulus movement. We will study the response to velocity of a large sample of cells in both the LGN and OT using the technique of extracellular microelectrode recording. We are particularly interested in studying the differential velocity preference of cells at a number of intensities and in determining the mechanism which is responsible for the differential velocity preference. Recordings will be made from both sustained (type X) and transient (type Y) cells at a range of retinal eccentricities. The mechanism responsible for differential velocity preference in these cells will be studied by determining the minimal region of the receptive field necessary for a cell to exhibit a differential preference for a particular velocity, by studying the spatial and temporal summation properties of these regions, and by comparing the response properties of cells in the lateral geniculate nucleus and the retina. An important contribution of this research is that it will provide a basis for understanding the differential velocity preferences of simple and complex cells in the primary visual cortex.